COPPER-CONTAINING KFI-TYPE ZEOLITE AND USE IN SCR CATALYSIS

Abstract

The present invention relates to a copper-containing KFI-type zeolite, wherein the zeolite contains 1 to 4.5 wt.-% copper. The invention is also directed towards a method for producing the copper-containing zeolite according to the invention as well as towards the use of the zeolite in SCR catalysis. Further subjects of the invention are a washcoat which contains the zeolite according to the invention, an SCR catalyst which contains the zeolite according to the invention as well as an exhaust-gas cleaning system which comprises the SCR catalyst.

Claims

1. A copper-containing KFI-type zeolite, wherein the zeolite contains 1 to 4.5 wt.-% copper relative to the total weight of the zeolite and wherein the zeolite is largely free of phases of the structure types CHA, ERI and LTL and has a phase purity >50%.

2. The copper-containing zeolite of claim 1, wherein the zeolite comprises primary crystallites with cuboid structure.

3. The copper-containing zeolite of claim 1, wherein the zeolite comprises primary crystallites with cubic structure.

4. The copper-containing zeolite of claim 1, wherein the zeolite comprises primary crystallites with a size in the range of from 0.2 to 10 m.

5. The copper-containing zeolite of claim 1, wherein the zeolite contains iron.

6. The copper-containing zeolite of claim 1, wherein the proportion of copper and iron together is 1.01 to 10 wt.-% relative to the total weight of the zeolite.

7. Copper-containing zeolite according to claim 1, wherein the zeolite has phase proportions of a zeolite of structure type MER.

8. (canceled)

9. A method for producing a copper-containing zeolite of claim 1, comprising: providing a KFI-type zeolite which can have phase proportions of an MER-type zeolite, thermally treating or hydrothermally treating the zeolite at a temperature 500 C.

10. The method of claim 9, wherein a replacement of copper and optionally iron takes place before the thermal/hydrothermal treatment or after the thermal/hydrothermal treatment.

11. The method of claim 10, wherein the zeolite is converted into the ammonium form before the copper and optionally iron are replaced.

12. The method of claim 9, wherein the thermal/hydrothermal treatment takes place over a period of from 30 minutes to 50 hours.

13. A method for conducting SCR catalysis using a zeolite of claim 1 as an SCR catalyst.

14. A washcoat containing a zeolite of claim 1.

15. A SCR catalyst containing a zeolite of claim 1.

16. An exhaust gas cleaning system containing the SCR catalyst of claim 15.

17. A SCR catalyst containing the washcoat of claim 14.

18. The copper-containing zeolite of claim 1, wherein the proportion of copper and iron together is 1.01 to 4.51 wt.-%, relative to the total weight of the zeolite.

Description

[0077] The invention will now be explained with the help of some embodiment examples which are not to be understood as limiting the scope of the invention. Reference is additionally made to the figures. There are shown in:

[0078] FIGS. 1 to 4 XRD spectra of a ZK-5 zeolite in the NH.sub.4 form as well as after calcination at 500 C. in the H form.

[0079] FIGS. 5 to 8 XRD comparison spectra of a KFI and an MER zeolite.

[0080] FIGS. 9 and 10 Toluene TPD spectra of an H-MFI (FIG. 9) and H-ZK5 zeolite (FIG. 10).

[0081] FIG. 11 the NO.sub.x conversion and the N.sub.2O formation of a Cu-ZK-5 zeolite according to the invention as a function of the temperature.

[0082] FIG. 12 a TEM picture of the Cu-ZK-5 zeolite according to the invention with cubic morphology.

EMBODIMENT EXAMPLES

Example 1

[0083] A Sr,K-ZK-5 zeolite was produced via a synthesis gel in which a solution containing potassium aluminate was mixed with a silica sol and a strontium nitrate solution. The aluminate solution was produced by dissolving Al(OH).sub.3 in aqueous potassium hydroxide (pellets, 85% dissolved in deionized water). This potassium aluminate solution was mixed with the strontium nitrate solution and a colloidal silica sol (e.g. AM-30, HS-30, HS-40 or LS-30) (Dupont). (Gel composition 2.3 K.sub.2O:0.2Sr(NO.sub.3).sub.2:1 Al.sub.2O.sub.3:12SiO.sub.2:160 H.sub.2O).

[0084] In a production variant (gel composition 2.3 K.sub.2O:0.1 Sr(NO.sub.3).sub.2:1Al.sub.2O.sub.3:10 SiO.sub.2:160 H.sub.2O) the aluminate solution was produced as follows: 1.149 g aluminium nitrate was dissolved in a solution containing 15.0 g deionized water and 6.463 g potassium hydroxide pellets. The aluminate solution was left to stand at 20 C. for two days until the wire was dissolved. The strontium nitrate solution was obtained by dissolving 4.455 g strontium nitrate (Sr(NO.sub.3).sub.2, 99%, Fluka) in 13.57 g deionized water. The Sr.sup.2+-containing silica solution was produced by adding strontium nitrate solution to 240.64 g Ludox AM-30. This suspension was then mixed with the aluminate solution. The resulting gel was shaken for six minutes. The crystallization was carried out at a temperature of 100-190 C. in a noble-metal autoclave. The products were filtered, washed with deionized water and air-dried at 120 C. Each example was measured with XRD.

[0085] The zeolite according to the invention can be produced very easily and economically, in particular by dispensing with costly organic templates, in contrast, for example, to SSZ-13 with CHA structure.

Example 2

Ion Exchange on ZK-5 Zeolites

[0086] Firstly, the zeolite produced according to the invention was converted into the ammonium form.

[0087] 130.0 g ammonium nitrate was dissolved in 1170.0 g demineralized water and 130 g zeolite powder was added. The suspension was stirred on a magnetic stirrer. Then the suspension was heated to 80 C. accompanied by stirring and the batch stirred for an hour. The suspension was then filtered off, the filter cake washed with demineralized water and the process repeated twice. The filter cake was then dried overnight at 120 C.

[0088] The KFI-type zeolite used according to the invention is characterized by a problem-free ion exchange compared with for example SAPO-34.

[0089] FIG. 1 shows a ZK5 zeolite after ion exchange in the ammonium form, wherein the proportions of the structure type MER can still be seen. FIG. 1 shows the section for 2 theta of 10-20. After the zeolite was thermally treated (calcined) for eight hours at 500 C., a clear decline in the MER phase can be seen, whereas the signals for the KFI phase remain virtually stable. This decline can also be seen in the sections for 2 theta of 20 to 30 and 30 to 40 (see FIGS. 2, 3 or FIG. 4 which shows the complete range).

Example 3

Copper Exchange

[0090] Batch size: 98.73 g

[0091] Cu content reference value [%]: 4.50

[0092] 98.73 g zeolite powder was suspended in 500 ml demineralized water. 41.52 g copper tetramine hydroxide was added to this suspension and the batch was stirred for 16 hours. The suspension was then filtered off and the filter cake washed with demineralized water. The process was repeated once.

[0093] The filter cake was then transferred to a porcelain dish and dried overnight at 120 C. The copper content was 4.1%.

[0094] The KFI-type zeolite used according to the invention is characterized by a problem-free ion exchange compared with for example SAPO-34.

Example 4

Production of a ZK5-Cu-Type Washcoat

[0095] 38.98 g of the produced zeolite powder was suspended in a beaker with 85 g demineralized water. 29.2 g silica sol (Bindzil 2034 DI) and 4.8 g nitric acid (65% p.a.) was then added to the suspension. The suspension was then ground in a mill.

Example 5

Measuring the NO.SUB.x .Conversion of the Cu-ZK-5

[0096] To determine the catalytic activity of the Cu-ZK-5 produced according to the invention a flow-through substrate (1 inch2 inch, 400 cpsi) was coated with a Cu-ZK-5-based washcoat according to the invention and the catalytic activity measured. FIG. 11 shows the NO.sub.x conversion of the Cu-ZK-5 under the test conditions: : 1.0, NO.sub.x; 500 ppm, GHSV=84000 l/h, O.sub.2, CO.sub.2 and H.sub.2O each 5 vol.-%, NO.sub.2/NO.sub.x=0.3.

TABLE-US-00002 Temperature C. NO.sub.x conversion NH.sub.3 slip [ppm] N.sub.2O [ppm] 194 0.27 355 10 215 0.65 143 11 276 0.91 7 17 323 0.92 4 16 374 0.90 4 12 426 0.88 5 11

Example 6

Measuring the N.SUB.2.O Formation

[0097] The N.sub.2O formation on the Cu-ZK-5 according to the invention was also examined. FIG. 11 shows the N.sub.2O formation of a Cu-ZK-5 produced according to the invention with 4.1 wt.-% copper. The chosen test conditions were as follows: : 1.0, NO.sub.x: 500 ppm, GHSV=84000 l/h, O.sub.2, CO.sub.2 and H.sub.2O each 5 vol.-%, NO.sub.2/NOX=0.3.

[0098] A far clearer advantage is seen with the small-pored zeolite as SCR catalyst. The quantity of N.sub.2O formed is very small and is in the same order of magnitude as with an iron-containing zeolite, while the small and medium-pored zeolites sometimes produce up to six times the quantity of N.sub.2O. Additionally, the copper-containing ZK-5 has important advantages vis--vis for example an Fe-ZK-5 zeolite already known in the literature. Copper-containing zeolites have a clearly higher low-temperature activity, which is a decisively positive factor in SCR catalysis.

[0099] The zeolite according to the invention also has a sufficiently high hydrothermal stability, compared with other small-pored zeolites such as for example MER or zeolite 3A.

Example 7

Adsorption Behaviour Vis--Vis Hydrocarbons

[0100] Due to its molecular-sieve action, the zeolite according to the invention displays very largely no adsorption of higher hydrocarbons, e.g. branched long-chain aliphatics or also aromatics.

[0101] Toluene TPDs were measured in order to demonstrate the difference in adsorption behaviour. An H-MFI and an H-ZK-5 were examined.

[0102] The measuring took place as follows:

[0103] The zeolite was heated in the inert gas stream and then charged with toluene. The sample was then heated and then an MS was used to register what quantity of toluene was desorbed at what temperature from the zeolite. The result is summarized in the following table and can also be seen in FIGS. 9 and 10:

TABLE-US-00003 Toluene desorption Toluene desorption Sample [mol] [mol/g sample] H-MPI 64 636 H-2K-5 0.518 5

[0104] It is seen that H-ZK-5 adsorbs almost no toluene, while with MFI, which has larger pores, approximately 120 times as much toluene was adsorbed.